The present invention relates to radio data transfer networks in general and, more specifically, to the integration of a radio local area network into a larger data transfer network offering global communication possibilities.
The rapidly developing and expanding telecommunication technology has reached a state in which there are technically advanced but mutually incompatible solutions available for different purposes. In general, telecommunication systems can be divided into two main groups, one group consisting of voice and facsimile transfer (telephone services), and the other group of fast digital data transfer between computers. Data terminals of the first group include telephones, voice mail systems, telephone answering machines, telecopiers and facsimile servers. Data transfer takes place mainly as circuit switched services, whereby digitized data are transferred at an even speed, 64 kbit/s at the most, and there are no sudden peaks in the transfer speed. In the second group, the data terminals include servers, printers, user stations and personal computers, and data transfer takes place as packet switching in local area networks and other corresponding networks at a speed which can be as high as 100 Mbit/s, but the data move in the form of bursts, with silence between them.
The field of telecommunications has become more complicated with the widespread use of data transfer systems based on mobile wireless stations. In view of data transfer, they belong to the group of telephone services, but particularly in digital cellular radio networks, it is also possible to offer many services which have been difficult or impossible to implement in PSTN networks (Public Switched Telephone Networks).
Because the main criteria on which the user estimates new data transfer systems are ease of operation, level of services and low operating costs, it is clear that many overlapping systems, each of which only implements part of the data transfer tasks required, do not represent an ideal solution. In the development of data transfer, the objective should be to harmonize devices and systems so as to improve the level of service, reduce overlapping and to increase capacity. The options available should include both fast data transfer in the form of bursts for large amounts of data, and temporally continuing, high quality telephone connection for communication between people. In order to shed light on the background of the present invention, certain prior art solutions regarding integration of data transfer and improvement of services are examined at first. In telephone communications, the most advanced modem technology is represented by digital cellular radio systems, in which a small, low-weight mobile station (mobile phone) can be carried along and used for establishing a telephone connection within the coverage area of the system. Mobility and the related localization and control of the mobile stations by the system, together with the advantages of digital signal processing, such as advanced message services and good encryption and identification possibilities make cellular radio systems a strong candidate to become the primary telephone communication system in the future, likely to spread all over the world in the course of time. In this application, the GSM system (Groupe Speciale Mobile), which is common particularly in Europe, is used as an example of a cellular radio system, but in view of the invention, it is not essential which system is concerned.
In relatively small areas, where there are many users and dense communications, cellular radio systems often encounter problems of capacity. Examples of this are city centers, office buildings and airports. In addition, in office environments where data transfer between data terminals close to each other is frequently required, it is not practical to route internal communications via an external system. A common solution has beed to build a wired local area network for high capacity data transfer, for example a network according to the registered trademarks Ethernet.RTM. or Token Ring.RTM., to which the data terminals are connected by means of a special network adapter, and in which packet switched data transfer protocols typical of each network are used for the packaging and transfer of data. The local area networks are often combined into larger entities by arranging the connections between them either by way of a general telephone network such as PSTN (Public Switched Telephone Network) or ISDN (Integrated Services Digital Network) or by way of faster networks developed especially for this purpose, such as the ATM (Asynchronous Transfer Mode) networks.
Nevertheless, local area networks of the wired type are inflexible in view of expansion and adaptation. One alternative solution has been RLAN, Radio Local Area Network, which is known from many embodiments. For example, the patent application WO 93/07684 (Sixtel S.P.A.) presents a wireless local area network (RLAN), in which each user station participating in network communications is associated with a radio adapter and radio transmitter/receiver, which has a radio connection to a certain number of fixed base stations (radio bases). The application suggests an interface in accordance with the DECT standard (Digital European Cordless Telephone) as the radio interface. In the construction according to said application, the base stations are connected by wires to a concentrator, from which there can be a further connection to an ordinary wired local area network.
Other solutions for wireless local area networks are known from the following patent applications:
* EP 483 545 (IBM)
A method for improving the utilization of frequencies in a system in which several base stations are connected to a wired local area network. In order to prevent overlapping transmissions, the base stations are arranged in a daisy chain, and a circulating token controls the order of transmission. PA1 An improved version of the previous method. PA1 A wireless local area network, in which the mobile stations can switch to another base station. The base stations are connected to each other and to the server that controls the operation of the system by means of a wired local area network, and mobility messages that describe the movement of the mobile stations cause rearrangement in the lists which are kept by the base stations and the server for routing the connections. PA1 A version of the previous method, in which the decision on switching the mobile station to another base station is based on beacon messages sent by the base stations and on measuring their level in the data terminals. PA1 a radio transmitter/receiver for offering a radio interface for the data terminals which are located in said radio local area network, PA1 a line transmitter/receiver for offering an interface to the switching centre of said general cellular radio network, which interface is essentially similar to the interface between the switching centre and the base station controller defined in said general cellular radio network, and PA1 means for carrying out the required protocol conversions between the data transfer protocols used in said radio local area network and data transfer protocols used in said general cellular radio network. PA1 the first data terminal, which starts the communication, establishes a connection with the first gateway computer, which controls the operation of the first radio local area network and notifies that it wants to establish a data transfer connection with a certain second data terminal, and also informs whether it wants a telephone connection or a slow or fast data connection, PA1 said first gateway computer determines, on the basis of information saved in its storage media, whether the said second data terminal is or is not in the same radio local area network as said first data terminal, PA1 if said first and second data terminal are in the same radio local area network, said first gateway computer routes the connection between them using the nodes which are in the first radio local area network, PA1 if said first and second data terminal are not in the same radio local area network, and said first data terminal has informed that it wants a telephone connection or a slow data connection, said first gateway computer directs the connection request to a certain switching centre of the general cellular radio system, PA1 if said first and second data terminal are not in the same radio local area network, and said first data terminal has informed that it wants a fast data connection, said first gateway computer directs the connection request via a certain other gateway computer to a certain general network intended for data transfer between computers, and PA1 if said first and second data terminal are not in the same radio local area network, but said second data terminal is in a certain other radio local area network, from which there is a connection to said first radio local area network by means of a certain third gateway computer and a certain general, wired network intended for data transfer between home and office data terminals, said first gateway computer directs the connection request by means of said third gateway computer and said general, wired network intended for data transfer between home and office data terminals to said second radio local area network.
* EP 539 737 (IBM)
* EP 605 957 (NCR International)
* EP 605 989 (NCR International)
It is a common feature of the patent applications described above that in the systems presented by them, the data terminals communicate with the base stations only, and radio connections between the data terminals are not used. A network of this kind is only a moderate improvement compared to ordinary wired local area networks, because the wiring of the base stations is nearly as inflexible as wiring that extends up to the data terminals. A different solution, called HIPERLAN (HIgh PErformance Radio Local Area Network), is known from the ETSI (European Telecommunications Standards Institute) publications ETR069, ETSI TC-RES, HIPERLAN Services and Facilities document: "Radio Equipment and Systems (RES) HIPERLAN Services and facilities/System Definition Document", February 1993. In this solution, the network consists of nodes, each of which is constituted by a radio transmitter/receiver, which can communicate with other corresponding devices. In practice, the properties required from a node include radio operations, signal handling capability and memory and thus its natural embodiment is a computer in which the radio components are incorporated. for example in the form of a PCMCIA (Personal Computer Memory Card International Association) card.
HIPERLAN is intended for arranging internal data transfer in an office environment, and its objective is to combine the high capacity of an ordinary LAN with the flexibility of wireless systems. The theoretical range of the radio equipment in each node is a maximum of 800 meters at a limited data transfer rate and about 50 meters at the full 20 Mbit/s transfer rate. There is no fixed structure, but the users can form an ad hoc network for an application when required. The nodes can move and they can be switched on and off. The publications also define special protocol converter nodes, by means of which the HIPERLAN network can connect to external networks of the standard ISO 8802, which include, among others, ordinary wired local area networks and so called city networks (MAN, Metropolitan Area Networks). Protocol conversions take place at the MAC or DLC interfaces (Media Access Control, Data Link Control), which are telecommunication concepts generally known to persons skilled in the art.
Because HIPERLAN is a local network solution, which operates only in a limited area, it is as such not a solution to the problem of extensive integration of data transfer services stated previously in this document. However, it is an essential component in the present invention, and its technical implementation will be explained in more detail in connection with the description of the invention.
One network which offers worldwide, fast data transfer service is Internet, a freely formed network based on packet switched transfer between computers connected to the network. Nevertheless, Internet cannot be used as a component of an integrated data transfer system of the future in its present form, because the addresses of the nodes or data terminals connected to it are defined in a hierarchical tree structure, in which a node is always situated under another node and the data coming to a node are routed via nodes that are above it in the hierarchy. Because it is an essential requirement of the integrated data transfer system of the future that the data terminals are mobile, a node should be able to change place from one branch of the routing tree to another. Fixed Internet addresses, like those used presently, do not support changing the place of nodes, but a new Internet protocol is being planned, and the functions defined in it enable a node to move from one branch of the routing tree to another, although its Internet Protocol Address (IP Address) does not change. The new protocol is called Mobile IP, and it is known from the publication Internet DRAFT, "IP Mobility Support", Internet Engineering Task Force (IETF) Network Working Group, May 1994.